Striking changes in volatile profiles at sub-zero temperatures during over-ripening of 'Beibinghong' grapes in Northeastern China.

The evolution of free and glycosidically bound volatile compounds in 'Beibinghong' (Vitis vinifera×Vitis amurensis) grape berries throughout on-vine over-ripening and freezing processes was studied in two vintages. The aroma profiles of 'Beibinghong' icewine berries were characterized by C6 compounds, higher alcohols and terpenoids in free fractions and carbonyl compounds, higher alcohols, C6 alcohols and terpenoids in bound fractions. With regard to free volatile compounds, there was a decrease in the concentration of C6 compounds, terpenols and norisoprenoids and an increase of terpene oxides during over-ripening process. A striking alteration of volatile profile occurred at sub-zero temperatures, particularly for the free fractions such as C6 alcohols, higher alcohols and oxidative terpene derivatives. These changes were attributed to a series of reactions (biotransformation, oxidation and anaerobic metabolism) induced by water loss and especially freeze-thaw cycles. PCA revealed temperature and rainfall affected the accumulation of volatile compounds during over-ripening processes.